P(A|B) means the probability A will happen given B has happened. P(AnB) is the probability both will happen, and P(B) is the probability B will happen.
You can figure out a formula from that, but here's the generally accepted one:
To get 10% of your calories from polyunsaturated fats you would need to eat 200 calories worth. So 1 serving of walnuts would give you 180 calories. So one serving of walnuts would be 9% of your daily calories.
